1. Field of the Invention
The present invention relates generally to a strip brush seal arrangement to effect a seal between a rotary shaft of a compressor, gas turbine engine, refrigerator, pump or the like, and a housing containing the rotary shaft therein. More particularly, this invention relates to a technical domain of strip brush seals in which a lifting portion located the free end side of the seal portion is arranged at an angle relative to the diameter surface of the rotary shaft in order to increase a lifting force and to decrease friction under relative movements.
2. Description of the Related Art
Related art of the present invention is found in U.S. Pat. No. 6,343,792, which discloses a strip brush seal device 100 as shown in FIG. 21. In the strip brush seal device 100 of FIG. 21, a plurality of circularly bent, thin strip brushes 109, also called “leaves”, are arranged along the circumference of a rotary shaft 120 to form an annularly-shaped body. The annularly-shaped strip brush 109 is capable of separating a high pressure region P1 from a low pressure region P2.
A plurality of the strip brushes 109 are arranged to form an annularly-shaped body as a whole wherein the outer perimeter edges of the strip brushes 109 are welded at soldering portions 105 in an integral manner. The annularly-shaped outer perimeter surface thus formed by the soldering portions 105 defines a mounting portion 104, by means of which the annularly-shaped is installed onto a housing 110. A back plate 102 is disposed on one side of the strip brushes 109 which is in the low pressure region P2 whilst a retainer plate 103 is disposed on the other side which is in the high pressure region P1. The back plate 102 and the retainer plate 103 provide supports on the both sides of the strip brushes 109, and the back plate 102 effects a seal against a fluid located in the high pressure region P1. At the same time a seal against leakage of the fluid to the low pressure side P2 between the back plate 102 and the rotary shaft 120 is effected by a plurality of the strip brushes 109 constituting the annular shape.
However, the strip brush 109 retains a curved surface protruding in the rotational direction of the rotary shaft 120. Furthermore, as the strip brush 109 is made rather rigid, the free end surface of the strip brush 109 fits the outer diameter surface of the rotary shaft 120 with a relatively large clearance therebetween. The large fit clearance makes it difficult to effect a seal against the fluid. Also the strip brush 109 is bent to a circular shape such that the free end tip is directed toward the center of the rotary shaft 120. If the strip brush 109 increases its rigidity, the strip brush 109 exhibits less elastic deformation. Therefore the sliding surface of the strip brush 109 is subjected to wear when the free end tip of the strip brush 109 comes in contact with the rotary shaft 120 because of a vibration of the rotary shaft 120 or the like.
Thickness of the strip brush 109 is 0.1 mm and since the clearance gap between adjacent surfaces of the densely packed strip brushes 109 is arranged small, losing the degree-of-freedom in the strip brush 109 may worsen its elasticity. In particular, when the strip brush seal device 100 is in a small diameter, a longitudinal length of the strip brush 109 also becomes short. As a result the strip brush 109 substantially loses its elasticity and increasing wear of the strip brush 109 widens the clearance gap, which even worsens the seal capability.
Alternative related art of the present invention is found as a strip brush seal device 100 shown in FIG. 22. Strip brush seal device 100 retaining the strip brush 109 has a similar arrangement to the strip brush seal device 100 of FIG. 21. Fit surface of the strip brush 109 mating with the outer diameter surface of the rotary shaft 120 disposes a step 130 thereon in the direction of rotation. The depth of the step 130 is denoted by H′. Since the step 130 is less than or equal to the thickness of the strip brush 109, e.g., 0.1 mm, the step 130 is too small to generate a substantial lifting force for the strip brush 109 to depart from the rotary shaft 120 when the fluid acts on the small step 130.
Also as the step 130 is disposed on the free end surface of the strip brush 109, employment of a thicker strip brush 109 makes it even more difficult to provide the strip brush 109 with a sufficient lifting force in order to lift the strip brush 109 off the circumference of the rotary shaft 120, when the relation between the rigidity of the strip brush 109 and the magnitude of the lifting force generated by the fluid is taken into account. Furthermore the step 130 on the thin strip brush 109, which requires precision machining, is not straightforward to manufacture. Use of the step 130 thus increases a machining cost and increases the production cost of the strip brush 109 after all.
Alternative related art of the present invention is found in the aforementioned U.S. Pat. No. 6,343,792, which discloses a strip brush seal device shown in FIG. 23. Strip brush seal device 100 shown in FIG. 23 has a similar arrangement to the strip brush seal device 100 of FIG. 21. In the strip brush seal device 100 of FIG. 23, strip brushes 109 are installed in a groove disposed in the housing 110. The strip brush 109 disposes a step 130 at the free end tip halfway in the axial direction. Since the strip brush 109 is formed halfway width of the strip brush 109, a fluid pressure exerted along the axial direction cannot provide the strip brush 109 with a sufficient lifting force.
In the strip brush seal device 100 shown in FIG. 21 through FIG. 23, as described above, a plurality of strip brushes 109 whose thickness is as small as 0.1 mm are densely piled to form an annularly-shaped body. The piled strip brushes 109 exhibit high stiffness. Therefore when the strip brushes 109 are subjected to a sliding movement relative to the rotary shaft 120, problems still remain in the strip brushes 109 in terms of elastic deformation and reduction of friction forces.
In addition with a strip brush seal comprised of strip brushes 109 which are circularly bent toward the opposite direction relative to the rotational direction, the step 130 disposed in the strip brush 109 cannot generate enough lifting force to lift the strip brush 109 off the rotary shaft 120 even when the fluid pressure acts on the step 130. Also disposing the tiny step 130 on the thin strip brush 109 alone can hardly exhibit a practical, lifting force. It implies that care for wear of the strip brush 109 is far from being sufficient. Fabricating the step 130 on an extremely thin strip imposes another technical difficulty.
The present invention is introduced to alleviate the above mentioned problems. A primary technical goal which this invention tries to achieve is to provide seal strips of a seal portion wiping against a rotary shaft with a lifting force in order to be lifted from the rotary shaft and to decrease friction therebetween, and to improve the seal capability by making use of a pressure generated at the seal portion due to a process fluid. Another technical goal is to simplify the manufacture of the seal strips disposing a lifting means and to decrease the production cost thereof.